Elevator systems include various control features. One such feature required by elevator codes is that power cannot be supplied to the motor used to propel the elevator car whenever a hoistway door is not properly closed. Typical elevator systems include hoistway door lock switches that provide an indication when a corresponding hoistway door is not locked. There are other conditions in which power to the motor must be interrupted to satisfy current code requirements. Whenever such a condition exists, the connection between an elevator drive and the motor is interrupted by opening switch contacts at that location. The switch contacts disconnect the motor from the elevator drive so that the motor cannot receive power from the drive.
One drawback associated with that approach is that it requires a relatively expensive set of contacts between the drive and the motor. Additionally the switch contacts require periodic inspection and maintenance, which introduces additional cost. The switch contacts must be able to disconnect the motor from the drive when one of the doors is opened or another safety device provides an indication that the motor should not be powered. Another feature of typical switch contacts between the drive and the motor is that they are tested to confirm functionality before and after each elevator run.